Caps for cervix uteri as a birth control means have been known for a long time and have been found among the artifacts of antiquity. It has been reported that Aetius of Amida suggested for this purpose the use of a pomegranate shell cut into a hollow cup, and that beeswax discs fashioned to fit over the cervix have been used in Europe.
Modern cervical caps comprise a pre-formed rubber cap that is positioned over the cervix uteri to act as a sperm barrier. Such caps are manufactured in several sizes to accommodate the various uterine sizes normally encountered; however, with such caps the fit for a particular individual is inexact and necessarily a compromise. As a result, these caps often become dislodged during coitus and have to be removed periodically to accommodate normal uterine discharges. Thus, such caps are inconvenient to use and have not achieved a high degree of reliability.
Premanufactured cervical caps with valves are also known and are shown in U.S. Pat. No. 2,836,177 to Sells, U.S. Pat. No. 3,952,737 to Lippert et al. and German Pat. No. 475,496 to Leopold. These caps also suffer from the aforementioned lack of stability and are subject to dislodgement during use.
U.S. Pat. No. 4,007,249 to Erb describes a technique for custom fabrication of a cervical cap having a valve that is inserted during manufacture. The manufacturing expedients disclosed in this particular patent contemplate the painting of a liquid, polymerizable elastomeric material onto the cervix uteri followed by the polymerization of the painted material or, in the alternative, the use of a mold which retains a liquid, polymerizable elastomeric material in contact with the exocervical surface until it is polymerized.
The former expedient is impractical because the surface to which the liquid, polymerizable material is applied is wet with mucus and quite slippery, thus the applied material would fall off the exocervical surface due to gravity before polymerization of the material could take place and, in any event, it would be impossible to control the thickness of the applied polymerizable material during in situ polymerization. A cervical cap having a relatively non-uniform thickness is undesirable, however, because it is unstable and is likely to be dislodged in use. The second expedient disclosed in the Erb patent would also produce caps having an undesirable variable cap thickness that is likely to bring about dislodgement.
A further shortcoming of the caps shown in the Erb patent is that the prefabricated valving means utilized are of the leaflet or flap type. In such valves a viscous droplet of cervical mucus could hold the valve in an open position for an undesirably long time period, thereby providing an access aperture for sperm and defeating the very purpose of the cap. Moreover, inasmuch as the polymerizable material of the cap is in a fluid state when it surrounds the prefabricated valve, some of the fluid material may become enmeshed with the valve and interfere with its intended valving action after the material has polymerized.
U.S. Pat. No. 4,007,249 to Erb also mentions a technique disclosed initially by F. A. Wilde in 1838 in Das Weibliche Gebar-Unvermogen according to which a cervical cap allegedly can be made from a special wax impression of the vaginal portion of the cervix. As recognized by Erb, such a technique cannot produce an identical, negative-image, cervix-conforming inside surface because the cervix would be deformed while the wax impression is being made. The uterus is suspended in the lower abdomen by ligaments, is easily movable, and would tend to move up into the abdomen even with a gentle force applied to the cervix. As a result, accurate registration would be prevented by such a movement with attendant lack of stability for the cervical cap produced in such manner.
The techniques described by Erb are also likely to suffer from the same drawback, albeit for a different reason. In particular, in practicing these techniques the vaginal wall has to be expanded using a vaginal speculum or similar implement in order to expose the cervix during cap molding. This expedient tends to distort the cervix as well, elongating it along an imaginary line between the tips of the inserted, open vaginal speculum blades and shortening the cervix along an imaginary line at right angles to the imaginary line between the tips of the speculum blades. The attendant cervical distortion exceeds the limits for prosthetic stability of the cervical cap that is produced.
Accordingly, while a stable, well-fitting cervical cap can be an effective birth-control device, prior to the invention described and claimed in copending U.S. patent application U.S. Ser. No. 108,319, filed on Dec. 31, 1979 now U.S. Pat. No. 4,322,463 it was not possible to produce a cervical cap that has the requisite stability against dislodgement and that can be worn for extended periods of time such as months, or even years, without removal. The present application discloses a further refinement of the aforementioned invention that enhances the stability of a cervical cap.